1. Field of the Invention
The present invention relates to biopolymer granules of xanthan gum type and to a process for the preparation thereof.
2. Description of the Prior Art
High molecular weight polysaccharides of microbial origin, or biopolymers, produced by fermentation of a carbohydrate which can be assimilated by suitable microorganism, are well known to this art. The most representative example of such polysaccharides is xanthan gum. Because of their thickening properties and their rheology, the polysaccharides have found a variety of applications, especially in the field of foodstuffs and in the building, paint, paper, textile, cosmetic and plant protection chemical industries, in water treatment and in the petroleum industry, for example, in the drilling and the enhanced recovery of oil.
For many applications, the biopolymer must be in the form of a slightly concentrated aqueous solution. It is known that the major disadvantage of biopolymer powders is the difficulty of rapidly dissolving them, even under high-shear agitation. If wetted too quickly, the grains or particulates in contact with water are enveloped within a thin jellified film and become agglomerated. These agglomerates, or lumps, surrounded with partially surface-swollen polymer, disaggregate and dissolve only with difficulty.
Moreover, the biopolymer powder, in the form in which it is currently commercially available, presents safety problems because of the fine particles thereof which form dust clouds.
Intensive investigations have been carried out for many years in an attempt to solve these problems. Different powder formulations, as well as liquid compositions having high active substance concentration, have thus been proposed. Powder formulations are described, for example, in published French Application No. 2,487,368 which recommends coating with a protective layer of a paraffinic material which is expelled in hot water, and in published French Application No. 2,516,527 which teaches the addition of a material which supplies water, or is capable of retaining it by adsorption, such as, for example, silica. To be effective, these solid formulations require relatively large amounts of an adjuvant, the presence of which can be deleterious in certain applications.
Liquid compositions may either be in the form of suspensions in an organic liquid in which the polymer does not dissolve (compare, for example, published French Applications Nos. 2,531,093, 2,540,879, published European Applications Nos. 0,016,640, 0,391,28), or in the form of emulsions (published French Application No. 2,548,676). Liquid compositions have the disadvantage of relatively high cost, because of having to store and transport a large quantity of liquid.
Therefore, serious need still exists for the availability of polysaccharides which are easy to use and which do not display the disadvantages above outlined.